Abstract: Degeneration of defined populations of central nervous system neurons contributes to the extra-pyramidal deficits and memory loss observed in patients with Alzheimer's Disease (AD) and Parkinson's Disease (PD). The molecular and cellular mechanisms resulting in neuron death in AD and PD are poorly understood. Preliminary data suggests that anomalies in the neuronal signal transduction pathways may be involved. The hypothesis to be tested is that neuronal signal transduction pathways are abnormal in neurodegenerative diseases and contribute to their pathogenesis. In particular, we propose to examine in detail the signal transduction pathways involving phospholipid-derived second messengers, and their role in AD and PD. In order to test the central hypothesis of this application, the following aims are proposed. Aim 1 will determine the quantitative changes in the phospholipase C signal transduction pathway in defined populations of central nervous system neurons from postmortem tissues of Ad, PD, and age-matched control patients. Phospholipase C substrates (polyphosphoinositides) and its end-products (diacylglycerol and inositol trisphosphate) will be quantitated by gas chromatography electron-capture detection and immunoassay. Phospholipase C levels will be quantitated and localized using biochemical, immunological, immunohistochemical, and molecular techniques. Aim 2 will quantitate the changes in the phospholipase A2 pathway in AD, PD and control brains. Phospholipase A2 substrates (phospholipids), end-products (unesterified fatty acids including arachidonic acid, as lysophospholipids), and arachidonic acid metabolites (cyclooxygenase and lipoxygenase pathways) will be measured with a combination of gas chromatography, mass spectrometry, and enzyme-immunoassays. Phospholipases A2 isoforms (low or high-molecular weight), cyclooxygenases and lipoxygenases will be identified and localized. Aim 3 will examine the regulatory components of the phospholipases signal transduction pathways in AD, PD and control brains. In particular, heterotrimeric G-proteins will be identified and localized by antibody- based and molecular methods. Aim 4 will determine the role of sphingomyelin hydrolysis and ceramide accumulation in neuronal death. Aim 5 will determine whether neuronal signal transduction pathways are abnormal in transgenic mice expressing a NFH/LacZ fusion protein and which accumulate Lewy Body-like inclusions in mesencephalic and telencephalic neurons as a function of age.